Learn about this topic in these articles:

role in Xerxes I’s invasion of Greece

...men according to Herodotus and 360,000 by modern estimate, supported by 700 to 800 ships. Their passage was facilitated by a massive engineering works: a channel was dug across the Isthmus of
Actium so that the peaks of Mount Athos might be avoided. Nevertheless, the army’s size was of no help, partly because of misinformation about the enemy terrain and partly because of the appearance...